The present invention relates generally to a process for selective photochemical etching of semiconductor materials in the manufacture of semiconductor devices. More particularly, the present invention is directed to a highly selective etching process for semiconductor materials in which regions of the semiconductor material surface with low minority-carrier lifetimes resulting from appropriate local impurity densities act as a self-aligned mask for etching using a carrier-driven photochemical etching reaction.
A most unique aspect of the present invention is the highly selective suppression of the etching of a region of a semiconductor surface by the deliberate localized introduction of relatively high concentration levels of impurity atoms. These impurity atoms, which may or may not be atoms of common dopant species, promote carrier recombination within the semi-conductor, thereby drastically reducing minority carrier lifetimes. These spatially localized regions of enhanced carrier recombination serve as a self-aligned mask during carrier-driven photochemical etching of the semiconductor material. Advantageously, various means for increasing the local impurity level may be employed.
In the fabrication of semiconductor devices, it is highly desirable to be able to produce self-aligned masks in the semiconductor material surface region itself in order to reduce the necessity for achieving exact registration and alignment of different masks for different steps in the total device fabrication process, which is a serious problem, and since, with the provision of self-aligning masks, fewer masking steps are required during device fabrication. However, known self-aligning technologies for semiconductor processing are generally applicable to only one semiconductor material and may furthermore require the employment of complex metallurgical techniques. Thus, there has remained a need for a process which is widely applicable to the entire range of elemental and compound semiconductors and, furthermore, for such a process which can be used with any carrier-driven photochemical reactions as may be developed for specific semiconductor materials. The present invention has as one of its objects the provision of such a process having wide applicability.
An ion-bombardment-damage controlled selective etching process has been previously proposed, however, such a process is of limited applicability, especially when the upper-most layer of a device structure must be very heavily doped, e.g. for semiconductor laser or SISFET structure fabrication. The present invention has as another of its objects the provision of a process by which the limitations inherent in the prior ion-bombardment-damage controlled etching process are advantageously overcome.
An important aspect of the present process which differs from the previous ion-bombardment-damage controlled etching process is that, in the present process, thermal treatment of the semiconductor material is required after ion implantation of impurities before any etching is performed.
Prior techniques for selective dry photochemical etching of semiconductor materials are known for example from U.S. Pat. Nos. 4,648,936 and 4,648,948 the disclosures of which patents are hereby incorporated herein by reference thereto.
Other relevant prior descriptions of photochemical etching processes for semiconductor materials are disclosed for example in Ashby, "Photochemical Dry Etching of GaAs", Appl. Phys. Lett. Vol. 45, p. 892 (1984); Ashby et al., "Composition-selective Photochemical Etching of Compound Semiconductors", Appl. Phys. Lett. Vol. 47, p. 62 (1985); Ashby et al., "Effect of the Band-gap Characteristics on Laser-induced Dry Etching of Semiconductors", Proc. 172nd Mtg. of the Electrochemical Society (Honolulu, October 18-23, 1987); and in Smith, R.A., Semiconductors, 2nd Ed., Cambridge Univ. Press, New York, 1978, p. 279, the disclosures of all of which are hereby incorporated herein by reference thereto.
Other conventional processes and techniques for masking and/or selectively etching semiconductor materials are known for example from U.S. Pat. Nos. 4,523,976; 4,595,454 and 4,599,136.
The process of the present invention for selective photochemical etching of semiconductor materials has the potential advantage of reducing the number of separate masking and mask-removal process steps inherent in conventional device fabrication techniques, thereby allowing for self-aligned structures with the associated advantages of eliminating mask registration errors, allowing for more densely packed semiconductor devices and higher performance semiconductor devices and circuits, and improving manufacturing yields. Further features, aspects and advantages of the process of the present invention will be made more apparent from the following detailed description.